Most modern transportation vehicles, agricultural tractors and implements, aircraft while performing surface conveyance (takeoff and landing), etc., are equipped with wheels having pneumatic tires inflated by a compressed fluid. Most frequently, the tires are inflated by compressed air, although some other media are used, such as water, in some agricultural applications.
Besides the main task - to insure reliable grip with the road surface - pneumatic tires also create a resilient connection between the vehicle and the road surface in which the resilience depends mainly on the pressure of air in the tire. The damping effect of this resilient connection is usually very small and is determined mainly by the damping characteristics of the tire material. As a result, when disturbances from the road have frequencies sufficiently higher than the natural frequency of the vehicle/tire system ("hop frequency"), the tires behave as vibration isolators, but for vibration frequencies close to the hop frequency, tires tend to worsen the vibration effect on the vehicle. If the vehicle has a suspension system, the harmful increases of the vibration effects on the vehicle when the frequency is near the hop frequency are alleviated, because the natural frequency of the suspension system is usually much lower than the hop frequency. However, even a limited increase of the vibration level at the tire's natural frequency is very unpleasant and in many cases can force the designer to lower the natural frequency of the suspension system. Especially bad consequences for the strength of the vehicle and its component units, passenger comfort, cargo conditions, etc., are encountered in cases when the tires are the sole resilient element, such as in wheeled tractors or bicycles. In such cases, the maximum speed of the vehicle while on a given road surface may be limited by the resonant amplitudes of vibration of the vehicle on tires. Increasing damping of the tires would reduce these resonant amplitudes and thus would alleviate the negative effects listed above as well as allow higher effective maximum speed.
This can be accomplished by providing a means by which a part of vibrational energy is dissipated (transformed to heat), thereby damping road-induced shocks and vibrations but which does not cause energy losses resulting from the rolling motion of the tire. Such means, proposed in U.S. Pat. No. 4,289,187 to E. Rivin (author of this invention), comprises a damping fluid chamber supported on the wheel and connected with the tire cavity by an energy-dissipating passage having a specified flow resistance. The system described in U.S. Pat. No. 4,289,187 was successfully tested as described in: B. Bachrach, E. Rivin, "Pneumatic Damping of Vehicle Tires to Improve Ride Quality", Proceedings of the Fifth International Conference on Vehicular Structural Mechanics, vol. P-144, SAE, 1984. While the positive effect of the system was demonstrated, its limitation was found to be a very small change of volume (and pressure) in the tire cavity when the wheel is subjected to vibratory loads. Only a 3% fraction of the tire reaction to its vibratory displacement caused by the road unevenness was found to be accommodated by the pressure change in the tire cavity. The bulk of the reaction is due to structural stiffness of the inflated tire and due to changes in the tire footprint area. Thus, while the system per U.S. Pat. No. 4,289,187 was proven to be useful, its performance capacity is rather limited. The performance capacity is also a function of volume ratio between the damping chamber and the tire cavity, thus the chamber has to be large to enhance the performance characteristics. Attachment of a large chamber to the wheel structure would require its expensive changes and is undesirable because of weight and packaging constraints.
While the role of vehicle tires in providing protection for passengers and cargo from the road-induced excitations is important, tires themselves may become sources of vibrations due to high-frequency acoustic resonance of their internal cavities. These resonant vibrations can be responsible for annoying components of noise in the vehicle passenger compartment. The frequency range of these annoying sound components is about 100-200 Hz, which is difficult to adequately isolate. An example of special means to reduce this noise is represented by U. S. Pat. No. 4,896,921 granted to C. Sato, et al. This patent teaches several chambers ("resonators") attached to the wheel and connected to the tire cavity though calibrated passages (similar to design of U.S. Pat. No. 4,289,187). Such design requires special and expensive wheel modifications. Other known designs, such as U.S. Pat. No. 4,909,295 granted to T. Nirei, et al, involve modifications to the tire structures, also rather expensive.